Record sheet

ABSTRACT

A record sheet comprising a base sheet and coated thereon a layer of a developer which produces a colored image upon reaction with a color former such as crystal violet lactone, said developer comprising (1) a metal compound of an aromatic carboxylic acid such as a reaction product of 2-hydroxy-1naphthoic acid and zinc chloride and (2) a metal salt such as copper sulfate or nickel sulfate. The developer has improved color developing ability and the colored image produced has increased resistance to light.

United States Patent [191 Kato et a1.

[451 Aug. 19, 1975 RECORD SHEET [75] Inventors: Hajime Kato; Takao Hayashi, both of Fujinomiya, Japan [22] Filed: Jan. 22, 1973 [21] Appl. No.: 325,720

[30] Foreign Application Priority Data Jan, 24, 1972 Japan 47-8830 [52] US. Cl 282/275; 428/537 [51] Int. Cl. B4lc 1/06; B4lm 5/00 [58] Field of Search 117/362, 36.8; 260/335 [56] References Cited UNITED STATES PATENTS 2,505,471 4/1950 Green 117/362 2,939,009 5/1969 Tien 1l7/36.2 3,418,250 12/1968 Vassiliades. 117/362 X 3,558,341 l/l971 Phillips 117/362 3,664,858 5/1972 Huffman 117/368 3,689,302 9/1972 Kubo et a1. 117/368 3,767,449 10/1973 Hayashi et a1. 117/362 3,769,302 10/1973 Hoover et a1. 260/335 3,772,052 11/1973 Kimura et a1 117/362 Primary ExaminerThomas J. Herbert, Jr. Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn and Macpeak [5 7 ABSTRACT A record sheet comprising a base sheet and coated thereon a layer of a developer which produces a colored image upon reaction with a color former such as crystal violet lactone, said developer comprising (1) a metal compound of an aromatic carboxylic acid such as a reaction product of 2-hydroxy-l-naphthoic acid and zinc chloride and (2) a metal salt such as copper sulfate or nickel sulfate. The developer has improved color developing ability and the colored image produced has increased resistance to light.

17 Claims, N0 Drawings RECORD SHEET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a record sheet, and more specifically to a record sheet utilizing an improved developer which produces a distinctive color upon reaction with a color former.

2. Description of the Prior Art Record sheets are well known which utilize the color reaction between an almost colorless organic compound (to be referred to as a color former hereinbelow) such as malachite green lactone, benzoyl leuco methylene blue, crystal violet lactone, Rhodamine B lactam, 3-dialkylamino-7-dialkylaminofluoranes or 3- methyl-2,2-spirobi(benzo[f] chromene), and an adsorbent or reactive compound (to be referred to as a developer hereinbelow) which produces a distinctive color upon contact with the color former. Color forrners can also be defined as electron-donating or proton-accepting colorless chromogenic materials and generally they are organic solvent-soluble, basic, substantially colorless organic compounds such as diarylmethane compounds, triarylmethane compounds, fluorane compounds, spiropyrane compounds and leucoazine compounds.

Examples of such record sheets include pressure-sensitive copying papers as are described, for example, in US. Pats. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457, and 3,418,250 and thermosensitive record papers as described, for example, in Japanese Patent Publication No. 4160/68 and US. Pat. No. 2,939,009. Further, a printing method is known which comprises supplying ink containing a color former to a sheet coated with a developer through a medium such as a stencil to thereby obtain a colored image, e.g., see German OLS No. 1,939,624.

In many instances, the color reaction which takes place between the color former and the developer requires pressure applied by a pen or typewriter, heat or ,some other altered physical condition.

As a typical embodiment of such a record sheet there are the pressure-sensitive copying papers. Pressuresensitive copying papers can be obtained by dissolving a color former in a solvent such as chlorinated diphenyl or chlorinated paraffin, dispersing the solution in a hinder or incorporating it into microcapsules, and then coating the dispersion or the microcapsular'solution obtained on a base material such as paper, a plastic film or a resin-coated paper.

A thermosensitive recording paper can be obtained by coating a color former and a thermofusible substance such as acetanilide on a base sheet. The thermofusible substance melts upon the application of heat and dissolves the color former.

The developer is usually dissolved or dispersed in water or an organic solvent along with a binder, and then coated on, or impregnated in, the base material. It can also be coated or impregnated as an ink just prior to recording.

Generally, the color former and developer are applied to the same or opposite surfaces of a base material, or to separate base materials.

Examples of the known developers are clays such as acid clay, activated clay, attapulgite, zeolite, or bentonite, organic acids such as succinic acid, tannic acid, gallic acid or phenolic compounds, and acid polymers such as phenol resins. The phenol resins have attracted attention as new developers (Japanese Patent Publication No. 20144/67), and a number of improved phenol resin developers have been proposed (U.S. Pats. Nos. 3,516,845 and 3,540,911 and British Patent 1,065,587).

The phenol resins are superior to many other developers in that when reacted with a color former they form a colored image stable to water, but they have the defect of insufficient color developing ability and give colored images which are poor in light resistance. For example, a colored image obtained by reaction of a phenol resin with crystal violet lactone readily fades when it is allowed to stand indoors or it is exposed to sunlight, and the surface of the phenol resin which has not participated in color production turns yellow.

Other acid polymers, such as a maleic acid-rosin resins or partially or wholly hydrolyzed styrene/maleic anhydride copolymers are impractical because of their inherent low color developing ability.

The inventors of the present invention previously suggested the effectiveness of metal compounds of aromatic carboxylic acids as developers for use in preparing record sheets. Various properties of the developer were thus substantially improved by using the metal compounds of aromatic carboxylic acids. However, there was still room for improvement as to their color developing ability and the light resistance of the colored images formed by the reaction of the developer with a color former. For example, the light resistance of a color image resulting from crystal violet lactone as a color former is improved, but the extent of improvement is inferior to that attained with benzoyl leuco methylene blue.

Accordingly, if the color developing ability of a re cord sheet utilizing a metal compound of an aromatic carboxylic acid upon contact with a color former can be improved, the commercial value of the record sheet would be further enhanced.

Furthermore, if the developing ability is increased, lesser amounts of the developer will give satisfactory developing ability, which makes it possible to lower the production cost and increase coating efficiency.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to increase the color developing ability of a metal' compound of an aromatic carboxylic acid.

A second object of this invention is to increase the light resistance of a colored image obtained using a metal compound of an aromatic carboxylic acid;

A third object of this invention is to provide a developer which meets the above objects.

Another object of this invention is to provide'a record sheet which meets the above objects.

The above objects of this invention can be achieved by incorporating a metal salt in a developer layer of a metal compound of an aromatic carboxylic acid in the preparation of a record sheet.

The record sheet of this invention basically comprises a base with a layer containing a metal compound of an aromatic carboxylic acid and a metal salt coated on the base material, and therefore can be in any form known in the art. For example, the developer and the color former may be applied to the same or opposite surfaces of the base, or to separate base sheets. It is also possible to store the developer in the form of ink, and

3 coat or print it on a base material as desired, whereby an image is immediately formed.

DETAILED DESCRIPTION OF THE INVENTION The metal compounds of aromatic carboxylic acids are, for example, zinc, tin, aluminum, nickel, magnesium and calcium salts of aromatic carboxylic acids, which are most preferred materials for use in the present invention. Specific examples of the aromatic carboxylic acids include benzoic acid, o-, mand pchlorobenzoic acids, o, mand p-nitrobenzoic acids, mand p-toluic acids, 4-metyl-3-nitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, 2,3-dichlorobenzoic acid, 2,4-dichlorobenzoic acid, p-isopropylbenzoic acid, 2,5-dinitrobenzoic acid, p-tert.-butyl-benzoic acid, N-phenylanthranilic acid, 4-metyl-3-nitrobenzoic acid, salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 3,5dinitrosalicylic acid, S-tert-butylsalicylic acid, 3-phenylsalicylic acid, 3-metyl-5-tert.- butylsalicylic acid, 3,5-di-tert.-butylsalicylic acid, 3,5- diamyl-salicylic acid 3-cyclohexylsalicylic acid, 5- cyclohexylsalicylic acid, 3-methyl-5-isoamylsalicylic acid, 5-isoamylsalicylic acid, 3,5-di-sec.-butylsalicylic acid, S-nonylsalicylic acid, 2-hyroxy-3-metylbenzoic acid, 2-hydroxy-5-tert.-butylbenzoic acid, 2,4-cresotinic acid, 5,5 -methylene disalicylic acid, 0-, mand p-acetaminobenzoic acids, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, anacardic acid, l-naphthoic acid, 2-naphthoic acid, 1- hydroxy-Z-naphtoic acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy-l-naphthoic acid, thiosalicylic acid, and 2- carboxybenzaldehyde. Of these, aromatic carboxylic acids having at least one hydroxyl group at one orthoposition to the carboxyl group prove effective, though both ortho positions can be substituted. Generally no more than two hydroxyl groups will be used as increasing numbers have a tendancy to lower water resistance. Also preferred are those acids which have an electronattracting group such as a halogen atom, an alkoxycarbonyl, an alkylcarbonyl group and like electron-attracting groups.

The aromatic ring of the aromatic carboxylic acid is preferably a benzene or naphthalene ring because as the number of rings increases the acids begin to become slightly colored. Further, the aromatic carboxylic acid preferably is substituted with an alkyl group because such a group advantageously solublizes the acid in an oily solution of color former. In this case, as the number of alkyl groups increases, synthesis of the acids becomes more complicated, and so the number of alkyl group is preferably no more than two for ease of synthesis. In the case where a substituent introduced into an aromatic ring is a hydrocarbon group such as an alkyl, aralkyl or aryl group, the number of carbon atoms thereof is preferably no more than 12 because the compound will gradually show weakened solubility in an aqueous alkali solution in the preparation of the metal salt thereof.

Examples of metals which constitute the metal compounds of aromatic carboxylic acids used in this invention are the metals of Group IB of the periodic table e.g., copper or silver, metals of Group IIA, e.g., magnesium and calcium, metals of Group IIB, e.g., zine, cadmium or mercury, metals of Group IIIA, e.g., aluminum or potassium, metals of Group IVA, e.g., tin or lead, metals of Group VIB, e.g., chromium or molybdenum, metals of Group VIIB, e.g., manganese, and metals of 4 Group VIII, e.g., cobalt or nickel. Ofthese, zinc and tin are especially effective.

The metal salt to be jointly used with the above described metal compound can be an inorganic or organic metal salt such as a salt formed between a metal and an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid, and a salt formed between a metal and an aliphatic organic acid such as acetic acid, citric acid, formic acid or oxalic acid. Although somewhat dependant upon the type of metal, the inorganic salts such as inorganic acid salts give especially good results. Additional examples of useful inorganic metal salts are the metal bromides, metal cyanides, metal iodides and metal sulfates. Examples of the metals that form the metal salt include copper, aluminum, manganese, nickel, silver, cobalt, and iron, and copper and nickel are especially preferred. Therefore, copper salts of inorganic acids and nickel salts of inorganic acids are the most preferred examples of metal salts used in this invention.

In this invention, the action of the salt between a metal and either an inorganic acid or aliphatic acid depends primarily on the metal and not on the inorganic or aliphatic acid used, so the acid selected is not limited. However, as the molecular weight of the aliphatic organic acid increases, the results become lessened because the amount of metal in the salt is lessened. Accordingly, one will generally use the lower molecular weight aliphatic inorganic acids as exemplified above.

Various methods can be used to produce the developer in accordance with this invention and apply it to a base material. However, since the effect or advantage of this invention is brought about if at least one metal compound of an aromatic carboxylic acid and at least one metal salt are jointly present in a developer layer, the method of preparation is not particularly limited.

Furthermore, the developer layer may contain an acidic resin such as a phenol-formaldehyde resin, an inorganic pigment such as a metal oxide, metal hydroxide or clay, or a chemically or physically treated produet thereof without appreciably impairing the advantages of this invention. The amount of these materials is generally 0.1 to 10 parts by weight based on 1 part by weight of aromatic acid. Specific examples of such ma terials are zinc oxide, titanium oxide, zinc hydroxide, zinc carbonate, acid clay, active clay, attapulgite, kaolin, etc. Other additives which increase the color developability are an adsorbent substance which has no color developing property in itself, such as agolmatolite or tale. The amounts which generally will be used are the same as those for the acidic resin above.

A coating solution of the developer according to this invention can be prepared by dissolving or dispersing at least one metal compound of an aromatic carboxylic acid and at least one metal salt in a solvent. When water is used as the solvent, there may be added a binder such as a latex, polyvinyl alcohol, a maleic anhydride/styrene copolymer, starch or gum arabic, and

5 solution coated on a support, it is not mandatory to use a binder.

lf desired, an ordinary developer such as acid clay or activated clay may be added in order to increase the developing ability, and an inorganic pigment may also be added in order to increase the adsorbing property of the developer. Other additives which increase the color developability are an adsorbent substance which has no color developing property in itself, such as agolmatolite or talc. The amounts which generally will be used are the same as those for the acidic resin above.

The coating solution obtained is coated on a base material such as paper, synthetic paper-like sheet or film in an amount such that it picks up at least about 0.1 g/m preferably from 0.5 to about 2 g/m of the metal compound of an aromatic carboxylic acid. The upper limit of the amount of coating is determined mainly by economic reasons, and therefore, greater amounts than the above-specified limit will not have any harm on the effects of this invention.

The amount of the binder to be used, although varying depending .upon the type of the binder, is preferably from 5 to 20 parts by weight based on 100 parts by weight of the metal compound of an aromatic carbox ylic acid. The minimum value of the binder is decided by the strength of the color developer layer. The maximum value thereof is decided by the color density desired.

The amount of the metal salt used is at least 0.1 part by weight, preferably from 0.5 to parts by weight, based on 100 parts by weight of the metal compound of an aromatic carboxylic acid.

Since the record sheet of this invention is characterized by a specific developer, other conditions such as the type of additives to be incorporated in the developer, the type and form of the color former, or the type of the solvent, are in accordance with the prior art heretofore described and can be easily chosen by those skilled in the art.

According to the invention, the light resistance of colored images is greatly increased and the developing ability of the developer is markedly improved. The developer of the present invention is especially effective when used with a combination of a primary color former having the ability to yield color instantaneously and a secondary color former having superior light resistance, as disclosed in U.S. Pat. No. 3,427,180.

The record sheet of this invention will be described in greater detail by the following Examples.

The effects obtained in these Examples were confirmed using a combination of an upper sheet prepared by coating a microcapsular solution containing a color former prepared in the manner described below on a base material and a lower sheet prepared by coating the developer of this invention on a base material.

Microcapsules containing a color former can be prepared by various methods. ln the following Examples, however, they were prepared by the specific method set out in the specification of U.S. Pat. No. 2,800,457 which is described below. Other encapsulation techniques which can be used are described in the following U.S. Patents: Nos. 2,800,458, 3,041,289, 3,116,206, 3,173,878, 3,190,837 or 3,265,630.

In the following, all parts are by weight, unless otherwise indicated.

Ten parts of acid-processed pig skin gelatin and 10 parts of gum arabic were dissolved in 400 parts of water at 40C, and 0.2 part of Turkey red oil was added as an emulsifier. Forty parts of a color former oil were emulsified in the resulting solution. The color former oil was a solution of 2% crystal violet lactone in an oil composed of 4 parts of chlorinated diphenyl and 1 part of kerosene. The emulsification was ceased when the size of the oil droplets became 5 microns on the average. Water at 40C was added to the emulsion to make the total weight 900 parts. At this time, care was taken not to lower the temperature of the liquid below 40C. Then, 10% acetic acid was added to adjust the pH of the liquid to 4.0-4.2 to cause coacervation. Stirring was further continued, and after 20 minutes, the liquid was cooled with ice water to gel the coacervate films deposited around the oil droplets. When the temperature of the liquid reached 20C, 7 parts of 37% formalin was added. When the temperature reached 10C, a 15% aqueous solution of sodium hydroxide was added to adjust the pH of the liquid to 9. The liquid was heated for 20 minutes with continued stirring to raise the temperature of the liquid to 50C. The temperature of the resultant microcapsular dispersion. was adjusted to C, and it was coated on a sheet of paper having a unit weight of g/cm in an amount of 6 g/cm as solids content, followed by drying.

A record sheet coated with microcapsules containing benzoyl leuco methylene blue was prepared in the same manner.

EXAMPLE 1 One gram equivalent of each aromatic carboxylic acid indicated in Table l was dissolved in 2 liters of a 2% aqueous solution of sodium hydroxide. Separately, one gram equivalent of each metal salt indicated in Table l was dissolved in 250 ml of warm water. The aqueous metal salt solution was poured with stirring into the aqueous sodium hydroxide solution of the aromatic carboxylic acid. Immediately, a metal compound of the aromatic carboxylic acid precipitated. The precipitate was filtered, washed several times with water, and dried to obtain a metal compound of the aromatic carboxylic acid.

Ten grams of each binder indicated in Table l was dissolved in 400 ml of each solvent indicated in Table 1, and g of the metal compound of the aromatic carboxylic acid obtained above and 2 g of each metal salt indicated in Table l which passed through a sieve with 325 mesh or smaller were dissolved or dispersed in the binder solution. The coating solution obtained was coated on a base paper having a unit weight of 50 g/m in an amount of 2 g/m as solids content using a coating rod, and dried.

EXAMPLE 2 0.1 g equivalent of each aromatic carboxylic acid indicated in Table l was dissolved in 200 ml of a 2% aqueous solution of sodium hydroxide by heating, and 100 g of a 10% aqueous solution of polyvinyl alcohol were added tothe resultant solution.

Then, 0.1 g equivalent of each metal chloride indicated in Table l was dissolved in 100 ml of warm water, and with stirring, the aqueous solution was added to the above solution. Immediately, a metal compound of the aromatic carboxylic acid precipitated, and the reaction liquid became turbid. 0.5 g of each metal salt indicated in Table =1 which had passed through a sieve of 325 mesh was dissolved or dispersed in the resulting dispersion. The resulting coating solution was coated on a base paper having a unit weight of 50 g/m in an amount of 3 g/m as solids content using a coating rod, and dried.

COMPARATIVE EXAMPLE 1 10 g of ethyl cellulose was dissolved in 400 ml of ethanol, and in this binder solution were dissolved or dispersed 100 g of the metal compound of the aromatic carboxylic acid obtained in Example 1. The resulting coating solution was coated on a base paper having a unit weight of 50 g/m in an amount of 2 g/m as solids content using a coating rod, and dried.

COMPARATIVE EXAMPLE 2 The dispersion of the metal compound of the aro matic carboxylic acid prior to the addition of the metal salt in Example 2 was used as a coating solution, and coated on a base paper having a unit weight of 50 g/m in an amount of 3 g/m as solids content using a coating rod, followed by drying.

COMPARATIVE TESTS A microcapsular sheet containing crystal violet lactone or benzoyl leuco methylene blue prepared as heretofore described was superposed on each of the sheets obtained in Examples I to 2 and Comparative Examples l to 2, and a color was developed by applying a pressure of 600 Kg/cm thereto.

The sheets were allowed to stand one day and one night in a dark place, and the reflection spectrum at a wavelength between 380 my. and 700 my. was measured by a Beckman spectrophotometer (Model DB).

8 The absorbance at the absorption maximum was made the fresh density of the developed color. The developed color was exposed to sunlight for 2 hours, and the reflection spectrum of the color surface was measured to 5 determine the density.

The fresh density of the developed color and the density measured after exposure to sunlight as described above are shown in Table l.

The results shown in Table 1 demonstrate clearly that 10 the addition of the specific metal salt to a developer layer containing the specific metal compound of an aromatic carboxylic acid leads to marked improvement in the color developing ability of the developer layer upon contact with benzoyl leuco methylene blue and 15 crystal violet lactone, and also to remarkably increased light resistance of the developed color image. In other words, the present invention makes it possible to apply the metal compound of an aromatic carboxylic acid more efficiently to a combination of a primary color 20 former which produces a color instantaneously, such as TABLE 1 Runs Aromatic carboxylic Metal Crystal violet lactone Benzoyl leuco methylene blue Nos. acid metal compounds salt Fresh Density af- Fresh Density after Aromatic metal density ter 2-hour density 2-hour exposure carboxylic salt exposure to to sunlight acid sunlight 1 3,5ditert. zinc copper 0.93 0.67 0.41 0.67

Ex. 1 butylsalisulfate sulfate cylic acid 2: copper 0.94 0.69 0.43 0.70

Ex. 1 chloride 3: nickel 0.96 0.75 0.28 0.51

Ex. 1 sulfate 4: 0.92 0.64 0.27 0.49

Com 1 5: Salicylic aluminum 0.97 0.65 0.25 0.48

Ex. 1 acid sulfate 6: copper 0.98 0.70 0.43 0.71

Ex. 1 sulfate 7: copper 0.97 0.69 0.41 0.69

Ex. 1 acetate 8: 0.95 0.62 0.24 0.45

Corn. 1 9: S-tert. Tin nickel 1.02 0.73 0.25 0.51

Ex. 1 butylsalisulfate nitrate cylic acid 10: S-tert. Tin manga- 0.99 0.69 0. 19 0.48

Ex. 1 butylsalisulfate nese cylic acid sulfate 11: copper 1.01 0.70 0.32 0.63

Ex. 1 sulfate 12: 0.98 0.65 0.09 0.38

Com. 1 l3: 3,5-ditert. zinc copper 0.95 0.69 0.43 0.70

Ex. 2 butylsachloride sulfate licylic acid [4; nickel 0.99 0.79 0.29 0.53

Ex. 2 sulfate 15; 0.94 0.65 0.26 0.48

Com. 2 16: Z-hydroxyaluminum 0.91 0.65 0.25 0.49

Ex. 2 l-naphthsulfate oic acid 17; copper 0.93 0.69 0.42 0.69

Ex. 2 sulfate 0.89 0.61 0.21 0.43

TABLE l-continued Runs Aromatic carboxylic Metal Crystal violet lactone Benzoyl leuco methylene blue Nos. acid metal compounds salt Fresh Density af- Fresh Density after Aromatic metal density tcr 2hour density 2-hour exposure carboxylic salt exposure to to sunlight acid sunlight Com. 2

Ex. Example; Com. Comparative Example What is claimed is:

1. A record sheet comprising a base sheet and coated thereon a layer of a developer which produces a colored image upon contact with an electron-donating colorless chromogenic material, said developer comprising l) a metal compound of an aromatic carboxylic acid and (2) from 0.5 to 10 parts by weight per 100 parts by weight of the metal compound l) of a salt of a metal.

2. The record sheet of claim 1 wherein (2) is a salt of a metal with an organic or inorganic acid.

3. The record sheet of claim 2, wherein said developer layer contains a binder in an amount of 5 to parts by weight per 100 parts by weight of the metal compound (1).

4. The record sheet of claim 2, wherein said aromatic carboxylic acid constituting the metal compound (1 is selected from the group consisting of benzoic acid, benzoic acid derivatives, salicylic acid, salicylic acid derivatives, naphthoic acids, anacardic acid, toluic acids and Z-carboxybenzaldehyde.

5. The record sheet of claim 2, wherein said aromatic carboxylic acid constituting the metal compound (1) is an aromatic carboxylic acid containing at least one hydroxyl group.

6. The record sheet of claim 5 wherein at least one hydroxyl group is at the ortho position to the carboxyl group.

7. The record sheet of claim 2, wherein said organic acid is an aliphatic organic acid.

8. The record sheet of claim 2, wherein the metal of said metal compound (1) is selected from metals of Groups IB, IIA, IIB, IIIA, IVA, VIB, V118 and VIII of the periodic table.

9. The record sheet of claim 8, wherein the metal is selected from the group consisting of copper, silver, magnesium, calcium, zinc, cadmium, mercury, aluminum, potassium, tin, lead, chromium, molybdenum, manganese, cobalt and nickel.

10. The record sheet of claim 2, wherein the metal of said metal compound (1) is zinc or tin.

1 1. The record sheet of claim 2, wherein the metal of said salt (2) is selected from the group consisting of copper, aluminum, manganese, nickel, silver, cobalt, and iron.

12. The record sheet of claim 2, wherein said salt (2) is selected from the group consisting of copper and nickel salts of inorganic acids.

13. The record sheet of claim 2, wherein said color former is a combination of a primary color former which yields a color instantaneously and a secondary color former which produces a color having fastness.

14. The record sheet of claim 13, wherein said color former is a combination of crystal violet lactone and benzoyl leuco methylene blue.

15. The record sheet of claim 2 wherein the aromatic carboxylic acid is substituted with an electron attracting group.

16. The record sheet of claim 2 wherein the aromatic carboxylic acid is from the benzene or naphthalene se ries.

17. The record sheet of claim 16 wherein the aromatic carboxylic acid is alkyl substituted. 

1. A RECORD SHEET COMPRISING A BASE SHEET AND COATED THEREON A LAYER OF A DEVELOPER WHICH PRODUCES A COLORED IMAGE UPON CONTACT WITH AN ELECTRON-DONATING COLORLESS CHROMOGENIC MATERIAL, SAID DEVELOPER COMPRISING (1) A METAL COMPOUND OF AN AROMATIC CARBOXYLIC ACID AND (2) FROM 0.5 TO 10 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OF THE METAL COMPOUND (1) OF A SALT OF A METAL.
 2. The record sheet of claim 1 wherein (2) is a salt of a metal with an organic or inorganic acid.
 3. The record sheet of claim 2, wherein said developer layer contains a binder in an amount of 5 to 20 parts by weight per 100 parts by weight of the metal compound (1).
 4. The record sheet of claim 2, wherein said aromatic carboxylic acid constituting the metal compound (1) is selected from the group consisting of benzoic acid, benzoic acid derivatives, salicylic acid, salicylic acid derivatives, naphthoic acids, anacardic acid, toluic acids and 2-carboxybenzaldehyde.
 5. The record sheet of claim 2, wherein said aromatic carboxylic acid constituting the metal compound (1) is an aromatic carboxylic acid containing at least one hydroxyl group.
 6. The record sheet of claim 5 wherein at least one hydroxyl group is at the ortho position to the carboxyl group.
 7. The record sheet of claim 2, wherein said organic acid is an aliphatic organic acid.
 8. The record sheet of claim 2, wherein the metal of said metal compound (1) is selected from metals of Groups IB, IIA, IIB, IIIA, IVA, VIB, VIIB and VIII of the periodic table.
 9. The record sheet of claim 8, wherein the metal is selected from the group consisting of copper, silver, magnesium, calcium, zinc, cadmium, mercury, aluminum, potassium, tin, lead, chromium, molybdenum, manganese, cobalt and nickel.
 10. The record sheet of claim 2, wherein the metal of said metal compound (1) is zinc or tin.
 11. The record sheet of claim 2, wherein the metal of said salt (2) is selected from the group consisting of copper, aluminum, manganese, nickel, silver, cobalt, and iron.
 12. The record sheet of claim 2, wherein said salt (2) is selected from the group consisting of copper and nickel salts of inorganic acids.
 13. The record sheet of claim 2, wherein said color former is a combination of a primary color former which yields a color instantaneously and a secondary color former which produces a color having fastness.
 14. The record sheet of claim 13, wherein said color former is a combination of crystal violet lactone and benzoyl leuco methylene blue.
 15. The record sheet of claim 2 wherein the aromatic carboxylic acid is substituted with an electron attracting group.
 16. The record sheet of claim 2 wherein the aromatic carboxylic acid is from the benzene or naphthalene series.
 17. The record sheet of claim 16 wherein the aromatic carboxylic acid is alkyl substituted. 